Techniques for build platform part release in additive fabrication and related systems and methods

ABSTRACT

According to some aspects, an additive fabrication device and a build platform suitable for use within an additive fabrication device are provided. The build platform may include a build surface on which material may be formed by the additive fabrication device when the build platform is installed within the additive fabrication device. According to some embodiments, the build platform may include a flexible build layer and at least one removal mechanism configured to be actuated to apply a force to the flexible build layer. Such actuation may cause the flexible build layer to deform, thereby enabling separation of material adhered to the build surface from the build platform. According to some embodiments, the build platform may comprise a restorative mechanism that acts to return the flexible build layer to a flat state so that subsequent additive fabrication may form material on a flat build surface.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit as a continuation under 35U.S.C. § 120 of U.S. application Ser. No. 15/835,163, filed Dec. 7,2017, which is hereby incorporated by reference in its entireties.

FIELD OF INVENTION

The present invention relates generally to systems and methods forseparating an additively fabricated part from a build surface.

BACKGROUND

Additive fabrication, e.g., 3-dimensional (3D) printing, providestechniques for fabricating objects, typically by causing portions of abuilding material to solidify at specific locations. Additivefabrication techniques may include stereolithography, selective or fuseddeposition modeling, direct composite manufacturing, laminated objectmanufacturing, selective phase area deposition, multi-phase jetsolidification, ballistic particle manufacturing, particle deposition,laser sintering or combinations thereof. Many additive fabricationtechniques build parts by forming successive layers, which are typicallycross-sections of the desired object. Typically each layer is formedsuch that it adheres to either a previously formed layer or a buildsurface upon which the object is built.

In one approach to additive fabrication, known as stereolithography,solid objects are created by successively forming thin layers of acurable polymer resin, typically first onto a build surface and then oneon top of another. Exposure to actinic radiation cures a thin layer ofliquid resin, which causes it to harden and adhere to previously curedlayers or the bottom surface of the build surface.

SUMMARY

According to some aspects, an additive fabrication device configured toform layers of material on a build surface is provided, the additivefabrication device comprising a build platform comprising a rigidstructure, a flexible layer attached to the rigid structure, whereinsome, but not all, portions of the flexible layer are attached to therigid structure, and wherein a surface of the flexible layer forms thebuild surface on which the additive fabrication device is configured toform layers of material, and at least one first mechanism configured tobe actuated to apply a force to the flexible surface, thereby deformingat least part of the flexible surface away from the rigid structure.

According to some aspects, a build platform for an additive fabricationdevice is provided, the build platform comprising a mounting attachmentconfigured to removably attach and detach the build platform to and fromthe additive fabrication device, a rigid structure coupled to themounting attachment, a flexible layer attached to the rigid structure,wherein some, but not all, portions of the flexible layer are attachedto the rigid structure, and at least one first mechanism configured tobe actuated to apply a force to the flexible surface, thereby deformingat least part of the flexible surface away from the rigid structure.

The foregoing apparatus and method embodiments may be implemented withany suitable combination of aspects, features, and acts described aboveor in further detail below. These and other aspects, embodiments, andfeatures of the present teachings can be more fully understood from thefollowing description in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments will be described with reference to thefollowing figures. It should be appreciated that the figures are notnecessarily drawn to scale. In the drawings, each identical or nearlyidentical component that is illustrated in various figures isrepresented by a like numeral. For purposes of clarity, not everycomponent may be labeled in every drawing.

FIGS. 1A-1D illustrate a schematic view of a build platform suitable foruse in an additive fabrication device, according to some embodiments;

FIGS. 2A-2C illustrate a schematic view of a build platform in which aroller mechanism actuates to apply a force to a build plate, accordingto some embodiments;

FIGS. 3A-B depict an illustrative stereolithographic additivefabrication device, according to some embodiments; and

FIG. 4 depicts an illustrative selective laser sintering additivefabrication device, according to some embodiments.

DETAILED DESCRIPTION

In additive fabrication, irrespective of the particular mechanism bywhich layers of material are formed, the material is usually formed onsome kind of surface usually referred to as a “build surface.” The buildsurface is typically part of a component of the additive fabricationdevice referred to as a “build platform.” The build platform may, insome additive fabrication devices, be configured to move within thedevice so that material can be deposited at an appropriate position onthe build surface. For instance, build platforms are frequentlyconfigured to move in a vertical direction between formation of eachlayer so that a new layer may be formed on top of a previously-formedlayer.

Typically, a first layer of material is formed on the build surface asan initial step of the formation process. The first layer may providestability for subsequent formation of additional layers and/or mayprovide a layer through which a part being formed may be adhered to thebuild surface. The degree to which the first layer and the build surfaceadhere to one another may depend on multiple factors, such as thematerial used to form the layer and the geometries of the build platformand/or the first layer. In some cases, the first layer of the part beingfabricated may have an area that is sufficiently small that the adhesiveforces between the first layer and the build surface during fabricationmay be insufficient to retain contact between the part and buildsurface, which may lead to the part separating partially or completelyfrom the build surface. Assuming the part successfully adheres to thebuild surface throughout the fabrication process, however, it is removedfrom the build surface as a post-processing step subsequent tofabrication of the part being completed.

In addition to removal of a part from a build surface, additionalpost-processing steps may be performed subsequent to fabrication of thepart. In some use cases, support material may have been formed for thepurpose of mechanically support overhanging or otherwise unsupportedstructures of the part during its fabrication, and this excess materialmay be removed (e.g., using a knife or other cutting tool). In some usecases, cleaning of a part may be performed after fabrication. Forexample, when using a photopolymer-based additive fabrication device itmay be beneficial to immerse a newly formed part into a cleaningsolution such as isopropyl alcohol to remove excess uncured or partiallycured resin from surfaces of the newly formed part. In some use cases,the surface of a fabricated part may be altered or finished usingtechniques that etch or otherwise affect the surface characteristics ofthe part. For example, parts fabricated using a fused filament additivefabrication technology may be finished using a vapor polishing technique(e.g., using acetone vapor) which causes the surface of the part to besmoothed and appear glossy. In some use cases, a part may be immersed inwater and/or an acid/alkaline solution (e.g., sodium hydroxide) todissolve a portion of the part.

Performing post-processing steps, including but not limited to thosediscussed above, may, however, risk damage to the fabricated part. Inmany cases, fabricated parts can be fragile and may include featuresthat could be damaged and/or removed by certain post-processing steps.For example, a user removing a support structure from a part or cleaninga part may exert a sufficient force upon the part (e.g., through holdingor otherwise) that the force causes the part to be damaged. In somecases, removing a part from a build surface to which it is adhered maycause damage to the part via the forces that are necessarily exerted onthe part in order to remove it. In some extreme cases, the use of ascraping or cutting tool to remove a part from a build surface mayresult in injury to a user. For example, if the adhesive forces betweena fabricated part and a build surface are sufficiently high, the usermay have to exert considerable force in order to separate the part fromthe build surface, which increases the risk of injury.

As a result of these and other challenges with post-processing, it maybe desirable to reduce adhesive forces between the part and the buildplatform during fabrication to make it easier to perform post-processingof parts after fabrication. However, such a reduction may cause a partto separate partially or fully from the build platform duringfabrication, typically causing the fabrication process to fail.Consequently, conventional processes and devices retain high adhesiveforces between the part and the build platform to ensure successfulfabrication yet resulting in post-processing challenges such as theaforementioned examples.

The inventors have recognized and appreciated that removal of a partfrom a build surface may be performed using one or more removalmechanisms that, when actuated, deform the build surface thereby causingthe part to separate from the build platform. The build surface may bethe surface of a flexible build layer that is fixed to the buildplatform in part whilst some portions of the build layer may be free tomove relative to a base portion of the build platform. For example, abuild layer may be fixed to the build platform around its perimeter (orsome portion of its perimeter) whilst an interior region of the buildlayer may not be affixed to the build platform and may be free to moveaway from the base. The removal mechanism may include any mechanismthat, when actuated, applies a force onto the build layer in a directionaway from a base of the build platform to which the build platform isattached. The removal mechanism thereby causes the build layer (andthereby the build surface) to deform, which in turn causes a partadhered to the build surface to separate from it.

According to some embodiments, a removal mechanism may comprise one ormore elements that can be moved towards and away from the build surface,such that actuating the mechanism causes the one or more elements topush at least a portion of the build surface away from the base to whichthe build surface is attached. Such actuation may be manual, such as viaa handle that can be pushed by a user holding the build platform, and/ormay be automatic, such as via one or more motors that operate to movethe elements to push the build surface.

According to some embodiments, a build platform may include one or moremechanisms, in addition to the removal mechanism(s), that apply arestorative force to the build layer. Since a flat build surface isdesirable for fabrication, such a restorative mechanism may act toreturn the build surface to a flat state after the removal mechanism isused to deform the build surface to remove a part. An illustrative usecase for a build platform so configured may, therefore, comprise acts offabricating a part on a flat build surface of a build platform,actuating a removal mechanism to deform the build layer and therebyseparate the part from the build platform, then manipulating the removalmechanism such that its force upon the build layer is sufficientlyreduced that a restorative mechanism can act to return the build surfaceto a flat state. A restorative mechanism therefore includes any elementsof the build platform that act to apply a force onto the build layer toreturn the build surface to a flat state.

In some embodiments, as an alternative to a restorative mechanism, thebuild layer may be formed from material that naturally returns to a flatstate when the removal mechanism is suitable actuated away from thebuild surface. For example, the build layer may comprise a rigidmaterial that buckles when force is applied to it by the removalmechanism, but that flexes back to its original state when the removalmechanism stops applying such a force.

According to some embodiments, a build platform of an additivefabrication device may be removable from the device. In some cases, thebuild platform containing one or more removal mechanisms may beconfigured to be attached to portions of the additive fabrication deviceduring fabrication and then removed from the device after fabrication.Separation of a part from the build platform may therefore, in at leastsome cases, occur when the build platform is separated from the additivefabrication device.

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, techniques for separating an additivelyfabricated part from a build surface. It should be appreciated thatvarious aspects described herein may be implemented in any of numerousways. Examples of specific implementations are provided herein forillustrative purposes only. In addition, the various aspects describedin the embodiments below may be used alone or in any combination, andare not limited to the combinations explicitly described herein. Inparticular, while the following describes embodiments in which removalmechanisms and/or restorative mechanisms may be located within a buildplatform, it may be appreciated that one or more components of suchmechanisms may be located within an additive fabrication device inproximity to the build platform and the same results achieved so long asthe appropriate forces, described below, can be directed to the buildsurface.

FIGS. 1A-1D illustrate schematic views of a build platform suitable foruse in an additive fabrication device, according to some embodiments. Inthe example of FIGS. 1A-1D, a build platform includes a rigid body 101coupled to a mounting attachment 102. In each of FIGS. 1A-1D, a buildlayer is affixed to the rigid body 101 at ends 107. The build surface ofeach illustrated build platform is the uppermost surface of the buildlayer.

FIG. 1A illustrates a build platform in an initial configuration whereinbuild layer 103 is flat (or substantially flat). FIG. 1B illustrates asecond configuration of the build platform in which the build layer 103is deformed by the application of force by removal mechanism 106. Ineach of FIGS. 1A and 1B, a restorative mechanism 104 applies a force tothe build layer.

FIG. 1C illustrates an alternate configuration of a build layer 104subsequent to application of force by removal mechanism 108. Whereas thebuild layer 103 shown in FIG. 1B deformed across its surface (e.g.,buckled) when the removal mechanism 106 applied a force to the buildlayer, the build layer 104 shown in FIG. 1C deforms primarily in alimited region of the build surface, as shown.

FIG. 1D illustrates another alternate configuration of a build layer 105subsequent to application of force by removal mechanism 110. In theexample of FIG. 1D, no restorative mechanism is included, accordinglythe build layer 105 may be configured to return to a flat (orsubstantially flat) state such as that depicted in FIG. 1A once theforce applied by the removal mechanism 110 drops sufficiently low forinternal forces within the build layer to cause the build layer todeform into a flat (or substantially flat) state.

Each of the build platforms shown in FIGS. 1A-1D may be utilized withinan additive fabrication device by arranging the build platform such thatmaterial is formed on the build surface of the build platform (i.e., theexposed upper surface of the build layer). In some embodiments, thebuild platform may be attached to the additive fabrication device viathe mounting attachment 102.

According to some embodiments, the build layer 103, 104 or 105 may beformed from one or more materials such that the build layer is flexibleor otherwise deformable. In some embodiments, build layer 103, 104and/or 105 may comprise a ferromagnetic layer, such as spring steel,such that the build layer is a flexible sheet of material. In someembodiments, additional layers may be added to such a ferromagneticlayer; for example, protective coatings and/or other materials may bedisposed upon the ferromagnetic layer that modify forces of adhesionbetween the build surface and material formed on the build surface.

In the example of FIGS. 1A-1C, forces may be applied to a build layer(e.g., build layer 103 and/or 104) by restorative mechanism 104, whichact to cause the build surface to adopt a substantially conformal shape.In some cases, such a shape may result in the build surface being flushagainst the rigid body 101. According to some embodiments, restorativeforces applied by restorative mechanism 104 may be applied across anyportion of the build layer, such as the entire surface or only a portionof the build surface on which material is expected to be formed duringadditive fabrication. In some embodiments, the restorative mechanism 104may comprise a single restorative force producing element (e.g., asingle magnet) or may comprise multiple restorative force producingelements that each produce restorative forces, which need notnecessarily be of the same magnitude nor produced by the same means(e.g., the restorative mechanism 104 may comprise any number of magnetsand/or springs coupled to the build layer).

Irrespective of how the restorative mechanism applies force to the buildlayer, according to some embodiments, the restorative mechanism mayapply force to the build layer such that there is no substantialdeformation of the build surface away from the rigid body 101 duringadditive fabrication process. That is, forces applied by the restorativemechanism to the build layer may be sufficiently high to overcome forcesapplied to the build surface in an opposing direction duringfabrication.

According to some embodiments, a build layer (e.g., build layer 103and/or 104) may be attracted and/or attached to the rigid body 101 baseby restorative mechanism 104 using any number of techniques, includingmagnetic, vacuum, adhesive and/or mechanical forces. For example, therestorative mechanism 104 may be coupled to the build layer 103 or tothe build layer 104 via one or more springs, magnetic clamps, magnets,low pressure volumes, adhesives, or combinations thereof. In someembodiments in which a build layer (e.g., build layer 103, 104 and/or105) comprises one or more ferromagnetic materials, a restorativemechanism may preferably comprise one or more magnets, such as one ormore sheet magnets.

According to some embodiments, a build layer (e.g., build layer 103, 104and/or 105) may be attached to rigid body 101 at one or more locationsso long as at least some of the build layer is free to move or deformsuch that the build surface changes shape. In the examples of FIGS.1A-1D, the build layers are attached to the rigid body at ends 107.Irrespective of where the build layer is attached to the rigid body, insome embodiments, such attachment may be via mechanical fasteners,magnets and/or adhesives. In some embodiments, a build layer may beremovably attached to rigid body 101 at one or both ends 107. Forinstance, one or more ends 107 of the rigid body may include a magneticelement of sufficient strength to hold the build layer in place duringfabrication whilst allowing a user to separate the build layer from therigid body via application of force.

In some embodiments, lifting of one end of the build layer may result ina progressive “peeling” of the build layer away from the rigid body 101that begins at the lifted end and that progresses across the rigid bodytowards an attached edge. This progressing peeling may tend to cause thebuild layer to adopt a bend at the propagating separation boundary,thereby potentially separating a part from the build layer.

FIGS. 2A-2C illustrate a schematic view of a build platform in which theremoval mechanism includes a roller which, when actuated, applies aforce to a build layer, according to some embodiments. As shown in theexample of FIGS. 2A-2C, a build platform 200 comprises a rigid body 201to which a build layer 203 is affixed at ends 207. A mounting attachment202 is coupled to the rigid body to allow the illustrative buildplatform 200 to be secured to an additive fabrication device. The buildplatform 200 further includes a magnetic element 205 that produces anattractive force upon the build layer 203.

When release of a part attached to the build layer 203 is desired, theroller removal mechanism 204 may be moved between the build layer 203and the rigid body 201. In the example of FIGS. 2A-2C, the roller 204 isconnected to a frame 208 which is in turn connected to a source oflinear motion. This source of motion may be generated manually by a userand/or automatically using, for example, one or more motors or otheractuators.

As it moves, the roller 204 may cause an area of the build layer 203 tomove away from the rigid body 201 so as to accommodate the space takenby the roller 204. The geometry of this region, or bend, depends uponthe degree of flexibility of the build layer 203, the geometry of theroller 204 and, as discussed below, the force with which the roller 204presses up against the build layer 203. Portions of the build layer 203outside of the region influenced by the roller 204 may remain conformalto the rigid body 201, held in place, at least in part, by forces suchas those caused by magnetic element 205.

As shown in the example of FIG. 2B, the region in which the build layer203 bends may be moved across the build layer as the roller 204 ismoved. As discussed above, the introduction and progression of the bendregion may tend to exert force(s) on material (e.g., a part) that isbonded to the build layer 203. Such forces may be effective in breakingsuch bonds without introducing unwanted distortions or risks of defectsto the part, particular in embodiments wherein parts may be attached tothe build layer 203 via a sacrificial layer known as a raft.

The inventors have observed that there may be a relationship between theradius of curvature of the bending portion of the build layer 203 andthe ability of the transiting roller 204 to cause parts with smallercross sectional attachment points onto the build layer to detach fromthe build layer. In particular, the amount of force generated by themotion of the roller 204 may be greatest when the part dimension alongthe axis of the bend is comparatively large as compared to the radius ofcurvature of the bend and smallest when the part dimension along thataxis is comparatively small as compared to the radius of curvature.Accordingly, it may be advantageous to minimize the radius of curvatureof the bend in some embodiments. For instance, the flexibility of thebuild layer may be increased so that the build layer more closelyfollows the shape of the roller, the roller's diameter may be reducedand/or the roller may be offset further from the rigid body 201.

In the example of FIGS. 2A-2C, a compressive mounting element 206 may beincluded in the mounting of a raised roller 204. This element serves toapply a force through the roller toward the build layer that changes asa function of the distance from the element 206 to the roller 204. Sinceit may be expected that it requires a greater force to displace buildlayer 203 close to its edges (as shown in FIG. 2A) than to displace thebuild layer towards its center (as shown in FIG. 2B), the compressiveelement allows the roller to extend toward the build layer until theupward force exerted by the compressive element 206 is equal to thedownward force exerted by the displaced build layer 203. Accordingly, inthe example of FIGS. 2A-2C, when approaching the midpoint of the rigidbody 201, as shown in FIG. 2B, the roller 204 reaches its maximumheight, deflecting the build layer 203. When approaching the edges ofthe rigid body 201, however, as shown in FIG. 2A, the roller 204 issituated closer to the rigid body compared with at the center becausethe forces that the build layer apply onto the roller toward the rigidbody are greater at the edge than at the center. Such a mounting elementmay have advantages over altering the dimensions and/or position of theroller 204, and/or increasing the flexibility of the build layer 203. Insome embodiments, the compressive mounting element 206 may comprise acompression spring and/or other type of spring.

According to some embodiments, compressive mounting element 206 mayallow for convenient positioning of the roller 204 to allow for a fullyflush build layer 203 when not in use, such as shown in FIG. 2C. Asshown therein, the compressive element 205 allows for the roller 204 tobe pushed below the primary plane of the build layer 203 and rigid body201 by the forces exerted by the build layer 203 near its attachmentpoint. Edges 207 may be further configured with a slope, curve, or othersuch features in order to guide the roller 204 into a recessed area ofthe rigid body 201 when moving towards the edge 207 and/or to guide theroller 204 away from such an area when moving towards the midpoint ofthe rigid body 201.

In some embodiments, frame 208 may be actuated in order to cause one ormore parts to detach from the build layer 203. Such actuation maycomprise any combination of automated, semi-automated or manualprocesses.

In some embodiments, the build platform may be mounted on or in apost-processing device configured to actuate the frame and mayoptionally perform other post-processing steps (e.g., cleaning a part onthe build platform, performing additional curing or heating, etc.). Themotion of the roller 204 discussed above may then be caused by one ormore linear motion sources of the post-processing device that areconnected to the frame 208. The success of such part removal may befurther determined based upon the measurement, by the post-processingdevice, of the motion and/or motive force of the frame 208 in rigidconnection to the roller 204. In particular, the presence of an objectadhered to the build layer 203 may, in many instances, increase theamount of force required to move the separation member 204 across thearea of the build layer 203 with such a part adhered. Thepost-processing device may then determine whether the part wassuccessfully removed by detecting the force measurement and identifywhether the force changed during separation, and if so, by how much. Insome cases, the post-processing device may then provide feedback to auser and/or a connected device reporting whether the part wassuccessfully removed.

In some embodiments, it may be particularly advantageous to actuate theroller 204 (e.g., by a post-processing device or otherwise) to moveacross the rigid body 201 and then reverse the motion to return it to astarting position. Forces and/or motion characteristics may then becompared between the two motions to determine if separation occurredduring the prior step, as discussed above.

In some embodiments, whether a part was successfully removed from thebuild platform may be determined by a post-processing device based uponthe weight of a part, wherein the part is automatically orsemi-automatically removed onto a platform capable of measuring theweight of any materials deposited onto it (which may be part of thepost-processing device or part of some other device). The movement ofthe roller 204 can thereby be repeated until the expected weight of thepart is detected on such platform or until a threshold for userintervention or alternative processing is reached.

According to some embodiments, various spaces between elements shown inthe example of FIGS. 2A-2C may be sealed to prevent or inhibit buildmaterial from entering such spaces. As one example, the inventors haverecognized that there may be advantages in preventing build material(e.g., liquid photopolymer, powdered nylon, etc.) from entering into thevoid formed by the roller 204 or to otherwise enter the space betweenthe build layer 203 and the rigid body 201. Accordingly, this space maybe sealed in various ways against the intrusion of build material.

According to some embodiments, edges 207 may be sealed in various ways,including the use of adhesives or other bonding materials, compliantgaskets, and/or other techniques. According to some embodiments, fillingof some gaps may be addressed by including side walls extending from theedges of the build layer 203 towards the rigid body 201. In someembodiments, such side walls may be left “open,” with sufficientrigidity to form a region closed on five sides and displacing any buildmaterial away from the void between the rigid body 201 and build layer203. In other embodiments, such side walls may connect with anotherenclosure, not shown here, in order to form a fully enclosed volume. Insuch embodiments, it may be further advantageous for side walls to beformed of a flexible and/or elastic material, such as an enclosing stripor skirt of polyethylene film, so as to allow for movement of the roller204 and any associated frame 208 elements.

FIGS. 3A-B depict an illustrative additive fabrication device comprisinga build platform configured as per any of the embodiments discussedabove. Illustrative stereolithographic printer 300 comprises a supportbase 301, a display and control panel 308, and a reservoir anddispensing system 304 for storage and dispensing of photopolymer resin.The support base 301 may contain various mechanical, optical,electrical, and electronic components that may be operable to fabricateobjects using the system. During operation, photopolymer resin may bedispensed from the dispensing system 304 into container 302.

Build platform 305 may be positioned along a vertical axis 303 (orientedalong the z-axis direction as shown in FIGS. 3A-B) such that the bottomfacing layer (lowest z-axis position) of an object being fabricated, orthe bottom facing layer of build platform 305 itself, is a desireddistance along the z-axis from the bottom 311 of container 302. Thedesired distance may be selected based on a desired thickness of a layerof solid material to be produced on the build platform or onto apreviously formed layer of the object being fabricated. In the exampleof FIGS. 3A-3B, the build surface of the build platform 305 faces in the−z direction, towards the container 302.

According to some embodiments, build platform 100, 120, 140 or 200, asshown in FIGS. 1A, 1B, 1C and 2A-2C, respectively, may be employed insystem 300 as build platform 305. In some embodiments, the buildplatform 305 may be removable from the printer 300. For instance, thebuild platform 305 may be attached to arm 315 (e.g., pressure fit orfastened onto) and may be removed from the printer so that a partattached to the build surface can be removed via the techniquesdescribed above.

In the example of FIGS. 3A-B, the bottom 311 of container 302 may betransparent to actinic radiation that is generated by a radiation source(not shown) located within the support base 301, such that liquidphotopolymer resin located between the bottom 311 of container 302 andthe bottom facing portion of build platform 305 or an object beingfabricated thereon, may be exposed to the radiation. Upon exposure tosuch actinic radiation, the liquid photopolymer may undergo a chemicalreaction, sometimes referred to as “curing,” that substantiallysolidifies and attaches the exposed resin to the bottom facing portionof build platform 305 or to an object being fabricated thereon. FIGS.3A-B represent a configuration of stereolithographic printer 301 priorto formation of any layers of an object on build platform 305, and forclarity also omits any liquid photopolymer resin from being shown withinthe depicted container 302.

Following the curing of a layer of material, build platform 305 may bemoved along the vertical axis of motion 303 in order to reposition thebuild platform 305 for the formation of a new layer and/or to imposeseparation forces upon any bond with the bottom 311 of container 302. Inaddition, container 302 is mounted onto the support base such that thestereolithographic printer 301 may move the container along horizontalaxis of motion 310, the motion thereby advantageously introducingadditional separation forces in at least some cases. A wiper 306 isadditionally provided, capable of motion along the horizontal axis ofmotion 310 and which may be removably or otherwise mounted onto thesupport base at 309.

FIG. 4 depicts an illustrative selective laser sintering (SLS) additivefabrication device comprising a build platform configured as per any ofthe embodiments discussed above. In the example of FIG. 4, SLS device400 comprises a laser 410 paired with a computer-controlled scannersystem 415 disposed to operatively aim the laser 410 at the fabricationbed 430 and move over the area corresponding to a given cross-sectionalarea of a computer aided design (CAD) model representing a desired part.Suitable scanning systems may include one or more mechanical gantries,linear scanning devices using polygonal mirrors, and/orgalvanometer-based scanning devices.

In the example of FIG. 4, the material in the fabrication bed 430 isselectively heated by the laser in a manner that causes the powdermaterial particles to fuse (sometimes also referred to as “sintering” or“consolidating”) such that a new layer of the object 440 is formed. SLSis suitable for use with many different powdered materials, includingany of various forms of powdered nylon. In some cases, areas around thefabrication bed (e.g., the walls 432, the platform 431, etc.) mayinclude heating elements to heat the powder in the fabrication bed. Suchheaters may be used to preheat unconsolidated material, as discussedabove, prior to consolidation via the laser.

Once a layer has been successfully formed, the build platform 431 may belowered a predetermined distance by a motion system (not pictured inFIG. 4). Once the build platform 431 has been lowered, the materialdeposition mechanism 425 may be moved across the fabrication bed 430,spreading a fresh layer of material across the fabrication bed 430 to beconsolidated as described above. Mechanisms configured to apply aconsistent layer of material onto the fabrication bed may include theuse of wipers, rollers, blades, and/or other levelling mechanisms formoving material from a source of fresh material to a target location.

According to some embodiments, build platform 100, 120, 140 or 200, asshown in FIGS. 1A, 1B, 1C and 2A-2C, respectively, may be employed insystem 400 as build platform 431. In some embodiments, the buildplatform 431 may be removable from the system 400.

Since material in the powder bed 430 is typically only consolidated incertain locations by the laser, some material will generally remainwithin the bed in an unconsolidated state. This unconsolidated materialis sometimes referred to as a “part cake.” In some embodiments, the partcake may be used to physically support features such as overhangs andthin walls during the formation process, allowing for SLS systems toavoid the use of temporary mechanical support structures, such as may beused in other additive manufacturing techniques such asstereolithography. In addition, this may further allow parts with morecomplicated geometries, such as moveable joints or other isolatedfeatures, to be printed with interlocking but unconnected components.

The above-described process of producing a fresh layer of powder andconsolidating material using the laser repeats to form an objectlayer-by-layer until the entire object has been fabricated. Once theobject has been fully fabricated, the object and the part cake may becooled at a controlled rate so as to limit issues that may arise withfast cooling, such as warping or other distortion due to variable ratecooling. The object and part cake may be cooled while within theselective laser sintering apparatus, or removed from the apparatus afterfabrication to continue cooling. Once fully cooled, the object can beseparated from the part cake by a variety of methods. The unusedmaterial in the part cake may optionally be recycled for use insubsequent fabrication.

According to some embodiments, a computer system may be providedsuitable for generating instructions to perform additive fabrication byan additive fabrication device comprising a removable build platform(e.g., build platform 100, 120, 140 or 200, as shown in FIGS. 1A, 1B, 1Cand 2A-2C, respectively). The computer system may execute software thatgenerates two-dimensional layers that may each comprise sections of theobject. Instructions may then be generated from this layer data to beprovided to an additive fabrication device, that, when executed by thedevice, fabricates the layers and thereby fabricates the object. Suchinstructions may be communicated to the additive fabrication device viaany suitable wired and/or wireless communications connection. In someembodiments, a single housing may hold the computing device and theadditive fabrication device such that the link is an internal linkconnecting two modules within the housing of the system.

According to some embodiments, it may be beneficial to both increase thestability and/or adhesion of a fabricated part to a build layer and toimprove the removability of the part by forming a structure, known as a“raft,” on the build layer (e.g., prior to forming the first layer ofthe body of the part). As discussed in U.S. patent application Ser. No.14/501,967, titled “Systems and Methods of Post-Processing Features forAdditive Fabrication,” filed on Sep. 30, 2014, which is herebyincorporated by reference in its entirety, such a raft structure may beadded to the part for fabrication and subsequently removed inpost-processing steps to leave only the desired part.

In some embodiments, a computer system configured to generateinstructions to perform additive fabrication may optimize a raftstructure in order to increase the effectiveness of part removal via theuse of a removal mechanism or other means of distorting the build layerIn particular, as discussed above, the forces applied against the baseof a part attached to a build layer depend in part on the relationshipof the radius of curvature of a bend in the build layer and thedimension of the part base along the axis of the bend. Accordingly, insome embodiments a computer system configured to generate instructionsto perform additive fabrication may generate raft structures having alength configured to be greater along the bend axis of the buildplatform, in order to increase the degree of force applied to the raftduring the removal process.

In some embodiments, a computer system configured to generateinstructions to perform additive fabrication may generate a raftstructure by taking into account a desired rigidity in a direction alongthe axis of the bend in the build layer during removal of a part. Forexample, the computer system may optimize a raft structure by increasingthe rigidity of the structure against bending forces in the axis of thebend in the build layer. Such increases in rigidity may advantageouslyincrease the amount of force potentially exerted between the bend in thebuild layer and the raft structure attaching the part to the buildlayer. For instance, generation of the raft by the computer system toincrease strength, such as by forming thicker regions, ribbing, or otherreinforcing structures, may help to counter this tendency, particularlyin instances wherein the build material may be comparatively flexible orhave low tensile strength.

In some instances, it may be further advantageous to conductpost-processing steps, such as thermal or actinic post curing of “greenparts,” appropriate to increase material strength or other propertiesprior to the application of removal forces. Alternatively, infabrication technologies utilizing multiple or variable propertymaterials, it may be advantageous to form one or more raft layers ofmaterials having increased rigidity and strength as compared to one ormore regions of the part.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andscope of the invention. Further, though advantages of the presentinvention are indicated, it should be appreciated that not everyembodiment of the technology described herein will include everydescribed advantage. Some embodiments may not implement any featuresdescribed as advantageous herein and in some instances one or more ofthe described features may be implemented to achieve furtherembodiments. Accordingly, the foregoing description and drawings are byway of example only.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. An additive fabrication device configured to formlayers of material on a build surface, the additive fabrication devicecomprising: a container; a build platform comprising: a rigid structure;a flexible layer comprising the build surface on which the additivefabrication device is configured to form layers of material; and arestorative mechanism configured to apply a force to the flexible layersuch that the flexible layer is held against the rigid structure by therestorative mechanism; and at least one source of actinic radiationarranged to direct actinic radiation onto a liquid photopolymer held inthe container to form the layers of material.
 2. The additivefabrication device of claim 1, wherein the restorative mechanismcomprises one or more magnets.
 3. The additive fabrication device ofclaim 2, wherein the restorative mechanism is arranged, at least inpart, within the rigid structure.
 4. The additive fabrication device ofclaim 1, wherein the flexible layer comprises a metal sheet.
 5. Theadditive fabrication device of claim 4, wherein the flexible layercomprises spring steel.
 6. The additive fabrication device of claim 1,wherein: the flexible layer comprises spring steel, the restorativemechanism comprises one or more magnets, and the one or more magnets arearranged at least partially within the rigid structure.
 7. The additivefabrication device of claim 1, wherein the restorative mechanismcomprises one or more springs.
 8. The additive fabrication device ofclaim 1, wherein the flexible layer is further coupled to the rigidstructure via one or more mechanical elements.
 9. The additivefabrication device of claim 8, wherein the flexible layer is attached tothe rigid structure via the one or more mechanical elements at opposingends of the rigid structure.
 10. The additive fabrication device ofclaim 1, further comprising at least one first mechanism configured tobe actuated to apply a force to the flexible layer, thereby deforming ata portion of the flexible layer away from the rigid structure.
 11. Theadditive fabrication device of claim 10, wherein the at least one firstmechanism is further configured to move relative to the flexible layerto vary a position of the portion of the flexible layer that isdeformed.
 12. The additive fabrication device of claim 1, wherein thebuild platform is configured to be removable from the additivefabrication device.
 13. A build platform for an additive fabricationdevice configured to form layers of material on a build surface of thebuild platform by directing actinic radiation onto a liquid photopolymerheld in a container, the build platform comprising: a mountingattachment configured to removably attach and detach the build platformto and from the additive fabrication device; a rigid structure coupledto the mounting attachment; a flexible layer comprising the buildsurface on which the additive fabrication device is configured to formlayers of material; and a restorative mechanism configured to apply aforce to the flexible layer such that the flexible layer is held againstthe rigid structure by the restorative mechanism.
 14. The build platformof claim 13, wherein the restorative mechanism comprises one or moremagnets.
 15. The build platform of claim 14, wherein the restorativemechanism is arranged, at least in part, within the rigid structure. 16.The build platform of claim 13, wherein the flexible layer comprises ametal sheet.
 17. The build platform of claim 16, wherein the flexiblelayer comprises spring steel.
 18. The build platform of claim 13,wherein: the flexible layer comprises spring steel, the restorativemechanism comprises one or more magnets, and the one or more magnets arearranged at least partially within the rigid structure.
 19. The buildplatform of claim 13, wherein the restorative mechanism comprises one ormore springs.
 20. The build platform of claim 13, wherein the flexiblelayer is further coupled to the rigid structure via one or moremechanical elements.
 21. The build platform of claim 20, wherein theflexible layer is attached to the rigid structure via the one or moremechanical elements at opposing ends of the rigid structure.
 22. Thebuild platform of claim 13, further comprising at least one firstmechanism configured to be actuated to apply a force to the flexiblelayer, thereby deforming at a portion of the flexible layer away fromthe rigid structure.